Abstract:
The rapid and selective detection of bacterial contaminations and bacterial infections
in a non-laboratory setting using advanced sensing materials holds the promise to enable robust
point-of-care tests and rapid diagnostics for applications in the medical field as well as food safety.
Among the various possible analytes, bacterial enzymes have been targeted successfully in various
sensing formats. In this current work, we focus on the systematic investigation of the role of surface
area on the sensitivity in micro- and nanostructured autonomously reporting sensing hydrogel
materials for the detection of bacterial enzymes. The colorimetric sensing materials for the detection
of β-glucuronidase (ß-GUS) from Escherichia coli (E. coli) were fabricated by template replication
of crosslinked pullulan acetoacetate (PUAA) and by electrospinning chitosan/polyethylene oxide
nanofibers (CS/PEO NFs), both equipped with the chromogenic substrate 5-bromo-4-chloro-3-indolylβ-D-glucuronide. The investigation of the dependence of the initial reaction rates on surface area
unveiled a linear relationship of rate and thereby time to observe a signal for a given concentration of
bacterial enzyme. This knowledge was exploited in nanoscale sensing materials made of CS/PEO
NFs with diameters of 295 ± 100 nm. Compared to bulk hydrogel slabs, the rate of hydrolysis was
significantly enhanced in NFs when exposed to bacteria suspension cultures and thus ensuring a
rapid detection of living E. coli that produces the enzyme β-GUS. The findings afford generalized
design principles for the improvement of known and novel sensing materials towards rapid detection
of bacteria by nanostructuring in medical and food related settings.
